1. Field of the Invention
The present invention relates to navigating through scenes containing three-dimensional objects and more particularly to viewpoint navigation in which a path through a scene is defined by a set of known viewpoints.
2. Description of the Prior Art
One of the difficulties users often face with a three-dimensional (3D) user interface is the task of navigating through scenes of objects. It takes some skill to learn and master the methods provided by each system, especially in systems that allow freeform xe2x80x9cflyingxe2x80x9d or xe2x80x9cwalkingxe2x80x9d in and around scenes. Though having many degrees of freedom may be considered to many a cumbersome and imprecise means of navigation, it is the method often used in many types of computer games and entertainment-based applications.
User interfaces with three-dimensional scenes for much more serious applications, such as controlling a factory or power plant, must be designed to be easy to navigate, predictable, controllable, and consistent. One way to accomplish this is through the use of viewpoint navigation in which a user""s path through a scene is defined by a set of known viewpoints. Viewing the scene at a particular viewpoint is determined by input from the user or possibly from externally generated events. This type of navigation is commonly found in Virtual Reality Modeling Language (VRML) sites on the World Wide Web.
The task of defining viewpoints is often the responsibility of the author, editor, or content developer. It is certainly possible to define viewpoints in a scene manually but is complicated by the fact that there are virtually an infinite number of possibilities. As an example, using a commercial 3D scene editor such as Kinetix 3D Studio Max, a camera viewpoint object may be inserted, positioned, and oriented in a scene. Of course, this requires a significant amount of skill to place and manipulate objects in a scene. Another method one might take is to specify coordinates and other parameters that describe a ViewPoint node such as in a VRML scene graph. However, working at the level of coordinate values and having no visual feedback requires even greater knowledge and experience of 3D systems.
The present invention greatly simplifies the problem of defining a set of viewpoints for a given scene of 3D objects. It is based on providing visual feedback as the viewpoints are defined as well as an automated process that can be practiced by novice and expert-level users. The present invention simplifies the problem by restricting the degrees of freedom available to the user through the use of a bounding surface (a viewpoint sphere), and by providing varying degrees of automation ranging from predefined viewpoints to generated tour paths, to interactive selection using free navigation.
The present invention includes three modes of operation that vary in ease-of-use and customization. The three modes of operation are: 1) completely automated calculation of viewpoints, 2) semi-automated selection through xe2x80x9ctoursxe2x80x9d, and 3) free navigation around a restricted viewpoint space. Given a set of 3D objects in a scene, the task is to generate a set of viewpoints using the present invention. The first step is to calculate the scene sphere, which is the minimum bounding sphere that contains the set of objects in the scene. The second step is to find the viewpoint sphere, which is done by calculating the viewpoint sphere radius. The user then chooses the mode of viewpoint selection as either completely automated, semi-automated, or free navigation. The output from the final steps is a set of viewpoints for the given scene of objects.